There’s plenty of blame to go round for this. Government departments are too unwilling to ask for outside advice and our political parties do a bad job of tapping academia for ideas. But, I think, the biggest problem is our academics. Far too many of them view policy as beneath them and any contact with government or politicians as contaminating.
Changing this culture will not be easy. But there are ways it can be done. For instance, the Research Assessment Exercise could take into account contributions to policy debates, advice given to government departments and the like. There also could be prestigious fellowships created to allow academics to do a year in government.
It is telling that when one thinks of the main academic influences on the likely next government of this country, they are nearly all American academics. Britain needs a proper ideas infrastructure.